1. Field of the Invention
This invention relates generally to a device for achieving transcutaneous laser photocoagulation of the retina, and more specifically, to a device which employs a high efficiency diode laser having a wavelength which is absorbed by the retinal pigment epithelium, enabling the device to be compact, portable, and used directly in the operating room.
2. Background of the Invention
As is known, human beings suffer from diseases, such as diabetes, which abnormally produce cells in the retinal pigment epithelium of the eye. These cells, after they are produced, will demand oxygen in order to survive, and the body will form new blood vessels in the eye to supply the newly-formed cells with oxygen. This process is known as neovascularization.
A problem is that the newly-formed blood vessels will, if their growth is left unchecked, damage the visible receptors in the retina, and the patient may lose sight. As a result, the medical profession and the laser industry collaboratively developed a technique called laser photocoagulation for checking the growth of the blood vessels.
Photocoagulation is simply the process of irradiating cells with laser light at a specific wavelength which is absorbed by the cells, causing a material in the cells to coagulate, and resulting in their ultimate death.
To destroy the blood vessels, the art developed a device employing an ion or dye laser for achieving photocoagulation. An ion or dye laser was chosen because the lasing materials used in such a laser, typically argon, krypton, or a dye, will have a wavelength which is absorbed by the hemoglobin in the blood of the blood vessel cells, causing the hemoglobin to coagulate, and the blood vessels to shrivel up and die. For example, an argon laser will produce laser light having a wavelength of either 488 nanometers (hereinafter "nm") or 514 nm, a krypton laser will produce laser light having a wavelength of 648 nm, and dye lasers will produce laser light having a wavelength range of 550-650 nm. Laser light having wavelengths approximately below 600 nm will be absorbed by the hemoglobin.
This device had then, and has now a significant number of problems, however. The predominant problem is that an ion laser is very inefficient, and the laser must be operated from a high voltage, three-phase outlet in order for it to produce laser light having enough intensity to achieve photocoagulation. Ion lasers, for example, have an efficiency level in the range of 0.1-2%, which means that only 0.1-0.2% of the input power is converted to useable laser light. To dissipate the heat which builds up from that portion of the input power which is not converted to useable laser light, a water or forced air coolant system must typically be added to the device. This results in the device being large and bulky, because of the coolant system which is required, and a device which is not portable, because it must be coupled to a special, high voltage, three-phase outlet in order to get the necessary input power. Moreover, because of its size, and lack of portability, the device cannot easily be brought into an operating room, making the use of this device in conjunction with retinal eye surgery inconvenient.
Another problem is that the device acts to suppress the growth of the blood vessel cells only, and does not act at all on the abnormal cells whose oxygen requirements results in the growth of the blood vessel cells in the first instance. As a result, after a particular treatment with the device is performed resulting in the clearing away of the blood vessels, the oxygen demands of the abnormal cells will still continue, and the body will respond by growing more blood vessel cells, necessitating additional treatments with the device.
Another problem is that the available options for delivering the light to the retina are somewhat limited. There are presently two known ways of delivering laser light to the retina: transpupilary and transcutaneous.
In the transpupilary method of delivery, laser light is delivered to the retina through the pupil, without requiring an incision in the eye. In the transcutaneous method of delivery, on the other hand, a cut is made in the eye, and a device known as an endoprobe is inserted, and used to deliver the laser light to the retina. The transcutaneous method of delivery is particularly advantageous when an incision has already been made in the eye in the course of eye surgery. In a surgery procedure known as a vitrectomy, for example, strands of solid material which have formed in the vitreous material between the lens and the retina are cut away, since otherwise, the strands may affect the vision and hurt the retina. During the course of a vitrectomy, it is a simple matter to insert an endoprobe in the incisions already made in order to photocoagulate portions of the retina. Since the ion laser device, as discussed above, cannot easily be brought into the operating room, it is difficult to use the transcutaneous method of delivery with the device.
Diode lasers have wavelengths which will be absorbed, and hence coagulate the retinal pigment epithelium cells, and destroy adjacent abnormal retinal cells. Krypton and long-wavelength dye lasers also are absorbed by the pigment cells. However, commonly available wavelengths are in the infrared portion of the light spectrum, i.e. in the range of 700-840 nm, which are not highly visible. As a result, it is difficult to position diode laser beams at the specific spot on the retina to be photocoagulated. The light produced by ion lasers, on the other hand, is visible, making it a relatively simple matter to track and position the laser beam. The result is that the art is and was discouraged from using, and did not in fact use, diode lasers for achieving photocoagulation. This is in spite of the fact that the use of such lasers would have had enormous beneficial consequences in that they could be used to destroy the abnormal retinal cells instead of just the problematic blood vessel cells, making further treatments unnecessary. In addition, krypton and long-wavelength dye lasers were available for this purpose.
Accordingly, it is an object of the present invention to provide a device for achieving transcutaneous laser photocoagulation of the retina which is compact, portable, and can be used in an operating room, and which achieves photocoagulation of the abnormal retinal cells through the use of laser light which is absorbed by adjacent pigment epithelium cells, and which provides a means for visibly tracking and positioning the laser beam onto the specific portion of the retina to be photocoagulated.